Abstract: On the basis of studying the historical development & present situation of Continuously Variable Transmission (CVT) at home & abroad, a new combined continuously variable drive scheme was designed, i.e. a hydromechanical CVT. The new CVT is composed of a Single stage Twinphase Torque Converter (STTC), Continuously Variable Chain Transmission (CVCT),reducing gears and their corresponding Hydraulic Clamping & Control Systems (HCCS). The new CVT is employed to improve the main drive of Shanghai 50 tractor which has a broad application and high market share. The comprehensive hydromechanical CVT with fair good performance has been laid out by using the thoughts and methods of Green Design & CAD. The torque converter can change the speed and torque automatically and steplessly as the working occasion demands. The driver can also adjust the CVCT by means of the HCCS and shift under load to change the speed continuously. Thus, automatical & controllable continuously varying speed can be realized, which ensures the diesel engine to work always around at the rated condition with the best fuel economy & power performance. The study & design showed that the newly designed CVT can be utilized to improve the overall operation performance of tractors and analogous vehicles such as fuel economy, power performance, driveability, comfortability, safety, acceleration, field crossing, less toxic exhaust emission, etc.